I'd guess "because we've always done it that way" is the most likely explanation. Highway road signs are a well studied counterpoint: mixed case has been shown to be essential. Never underestimate inertia in design.
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mswJul 20 '12 at 11:45

I would say the simple reasoning is that bold capital letters are easier and quicker to interpret at a glance than lower case letters.
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Liam SpencerJul 20 '12 at 12:01

2

If they are harder to read, then why would they be easier to interpret at a glance?
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Bart GijssensJul 20 '12 at 12:10

There are a lot of assumptions that uppercase is harder to read, but is that really true? That uxmovement link you cite is really just opinion masquerading as research. There isn't any evidence in there citing that uppercase is harder to read. However, a bit of research does loosely support that statement - see this interesting post over on skeptics.stackexchange. I think it's one of those issues that we just assume to be the case when infact it may actually not be.
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JonW♦Jul 21 '12 at 16:44

5 Answers
5

I believe it is in part because text in all-caps have a clear, regular rectangular shape to them regardless of the word or language, making them easier to position uniformly on any shape. That is, there are no descenders or ascenders to accommodate as there would be with lower-cased words (the position of which might vary depending on the word or language). This means that the controls can be designed in isolation without having to be concerned by what the label will be, since a simple rectangular area can be demarcated for the label.

Furthermore, accommodating any ascenders and descenders would also mean the overall lettering would have to be smaller, making the usually relatively small text on the controls potentially even harder to read.

It's exactly that with regard to space with camel cased characters. If it's a small button (which there inevitably will be, especially on the dash) and the lower case letters are proportionate to their capital counter parts they could be difficult to read. It would also look awkward if some buttons were all caps and some were mixed case, conveying an importance to certain buttons that may or may not exist.

I think a lot of manufacturers have shifted towards more image/icon related buttons (i.e. the fan is a blower, the seat controls are in the form of the seat) where they can because it's more appealing than all caps.

As an aside, with the proliferation of screen technology (ex: Ford's customizable digital dash and driver controls) I think you'll see more lower case type coming back.

Use of images & icons instead of text, especially by multinationals, probably has as much to do with reducing the burden of internationalization and localisation of the text - an icon can (if well chosen) work intuitively for many cultures
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ParanoidMikeAug 2 '12 at 14:28

I was always taught to use block capitals when something had to be clearly read. For instance, on prompt cards for use in a presentation. I think it's also because it looks more modular and symmetrical.

The appearance of upper case being more modular / symmetrical is actually a good thought, however I don't think I'd agree with your first point that they'd be used when something has to be clearly read - as pointed out in the OPs post; it's actually harder to read block-capitals quickly compared to standard text.
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JonW♦Jul 21 '12 at 16:30

@JonW - Your assertion seems correct in relation to extended passages of text. But for short fragments like those depicted in the photo, the text is short enough to be easily assimilated at a glance. The points made by Danny Varod and Graham Odds are pretty much on the money.
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Erik KowalApr 18 '14 at 12:43

But if you use uppercase for all words, how does that make words more prominent?
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Bart GijssensOct 18 '12 at 13:00

@BartGijssens IF ALL WORDS WILL BE UPPERCASED THAN IT WILL MORE PROMINENT THAN USER USED TO READ. BUT IT IS HARD TO READ FOR USER. IMAGINE IF ALL THE WORDS IN THE BOOKS WILL BE UPPERCASED. Natural case of letters is easier to read.
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webvitalyOct 19 '12 at 7:25